Acclaimed author David Sibley shares some insights into his newest work.
Interview by Katrina Marland

David Allen Sibley has harbored a fascination with trees and birds since childhood. (Credit: Erin Hartman)

David Sibley, well-known for the illustrations and identification skills exhibited in his exceptional book The Sibley Guide to Birds, has taken his work in a new direction: trees!

This fall, just in time for your last-minute Big Tree nominations, The Sibley Guide to Trees made its debut to great critical acclaim. The guide, a wealth of knowledge on tree identification, is crafted in Sibley’s aesthetic and easy-to-understand style. Excited about this great new book, American Forests interviewed the man behind the guide.

Q: Your previous guide was geared toward birds. Could you explain why you felt passionately enough about that subject to write and illustrate an entire guide?

A: Like many people, I’ve always been fascinated by birds. They’re fun to watch, always surprising, and identifying them in the field is challenging, so there’s always something to strive for, some mystery to be solved. For me, the field-guide project was all about learning (and making sense out of) all the variations in birds. I really enjoy those moments of discovery when one little fact falls into place and reveals a much larger pattern. And that’s what birding, and the years of putting together the bird guide, provided again and again.

Q: What made you decide to change your focus from birds to trees for your next book?

A: I was attracted to the challenge of sorting out the big patterns in another group besides birds, and really wanted to work on another big project where I could make discoveries and learn new things. I chose trees because they were around me all the time, easy to see, and possible to identify from a distance; in that sense tree-watching is similar to bird-watching. I also thought there was an opportunity to make a real contribution simply by producing a guide to trees that took a different approach.

Q: What sets this tree guide apart from the rest?

The Sibley Guide To Trees can help you learn to identify more than 600 tree species by bark, leaves, or a number of other characteristics.

A: I tried to create a tree guide that was similar in its approach and style to modern bird guides. Trees are so easy to study that most existing field guides emphasize close-up features like bud scales or leaf hairs. I wanted to emphasize things that could be seen at a distance, the same way I identify birds. The heart of the book is the illustrations; readers should be able to simply flip through the pages looking for a picture that matches their observation, rather than working with a text-based key. Also, the book is arranged taxonomically, with related species together. I think one of the goals of nature study is to develop an understanding of the larger patterns, and readers of this book should develop a sense of the similarities and differences between poplars and willows, or white oaks and red oaks, etc. simply by flipping through the pages and seeing those species together.

Q: What challenges did you encounter in compiling this tree guide?

A: Aside from the taxonomic challenges, I’d say the toughest thing was dealing with the scale of the illustrations. In the bird guide I simply painted the entire bird for each species, but if I tried to paint an entire tree showing the details necessary for identification, each painting would have had to be at least 10 feet tall! It took a long time to work out which parts of the tree to paint, what size to paint them, and how to arrange them on the page.

Q: We recently had a series of taxonomic changes to our National Big Tree Register, mostly involving the hawthorn genus, which inspires the next question: How did you decide what species and subspecies to include?

A: This was a very big challenge. First, I had to decide where to draw the line between trees and shrubs, and then I had to come up with a list of species and subspecies. I started with Elbert Little’s list of North American trees, and then modified that based on the Flora of North America project, the USDA Plants database, and John Kartesz’s Biota Of North America Program (BONAP) data. This was also modified by new research in a few cases, but there will always be disagreement and debate about these questions. I think the existence of variation within species is more important than the names or status given to those variations, so I simply tried to illustrate or describe all of the subspecies and to mention any debate over status.

The hawthorns are a special case, with 100 to several hundred species, depending on who you ask, so I took the easy way out by illustrating about 30 of the most widespread and distinctive forms. Maybe in a future edition I’ll be able to give them more comprehensive coverage, but I think it will be a long time before the differences are sorted out and botanists can all agree on a list of hawthorn species!

Q: What resources did you use to complete the guide?

Sibley’s guide features detailed illustrations to help would-be identifiers. (Credit: David Allen Sibley)

A: I tried to learn from all of the existing tree guides and many other field guides before I started work on this book; picking and choosing the features that I liked, and deciding how to incorporate them.

The field research was helped enormously by the fact that the Arnold Arboretum and Mount Auburn Cemetery are located here in Boston, so I could see a lot of different trees close to home. For the paintings and text, I used my own photos, sketches, and notes, along with lots of books and online references, which are mentioned in the guide’s acknowledgements – including, of course, American Forests’ National Register of Big Trees.

Q: You have been an advocate of conservation, especially on behalf of birds. Can you tell us more about the efforts you’ve made toward conservation, and the role that trees and forests have played in them?

A: Working on this book for the last seven years has really broadened my environmental view. I have always known that diverse and healthy forests are essential as habitat for birds and other animals, but it wasn’t until I started looking carefully at trees that I realized how much forests have changed in the last few centuries. It’s easy to look at birds and imagine that they are the same species that Audubon or even Columbus would have seen, following the same migration paths and timetables. But during that time period, the trees have changed dramatically. When you consider the clearing of forests, introduced diseases, and introduced trees, the forests in the eastern U.S. today are fundamentally different from those that early European settlers saw.

In that and many other ways, I think one of the big insights we can gain from looking at trees is that the boundary between natural and human habitats is completely blurred. Our lives are intertwined with the trees. There isn’t a natural world and a man-made world; it’s all part of the same system. What happens in Alaska affects us in New England, and what we do in our backyards is connected to everything else.

This article was published in the Autumn 2009 issue of American Forests magazine.